Single-Dose RSV Vaccine Efficacious in Protecting Older Adults for 2 Seasons

A single dose of the respiratory syncytial virus (RSV) prefusion F protein-based (PreF3 OA) vaccine offers older adults protection against RSV-associated lower respiratory tract infection (LRTI) over the course of 2 RSV seasons. Revaccination at 1 year is also well tolerated, but does not appear to provide additional efficacy benefit. These study results were published in Clinical Infectious Diseases.

In an ongoing phase 3, randomized, placebo-controlled trial (ClinicalTrials.gov Identifier: NCT04886596), researchers evaluated the efficacy and safety of 1- and 2-dose regimens (first dose followed by revaccination at 1 year) of RSVPreF3 OA against RSV-LRTI over 2 RSV seasons. Between May 2021 and January 2022, patients aged 60 years and older were randomly assigned 1:1 to receive either 1 vaccine dose or placebo prior to the first RSV season. Vaccine recipients were then re-randomly assigned 1:1 to receive either a second vaccine dose or placebo prior to the second RSV season. Patients who received placebo initially also received placebo prior to the second season to maintain blinding.

Secondary outcomes of interest included the efficacy of both vaccine regimens in preventing severe RSV-LRTI, RSV-associated acute respiratory illness (ARI), and RSV-LRTI by subtype, season, year, patient age at receipt of dose 1, comorbidities, and frailty. The safety of both regimens was also evaluated.

Of 24,967 patients comprising the modified exposed population, 6227 received 1 vaccine dose, 6242 received 2 doses, and 12,498 received placebo. Baseline characteristics were well balanced between the groups, and the median follow-up period from day 15 post-dose 1 until the end of second RSV season was 17.8 months.

The researchers confirmed the sustained efficacy of a single RSV dose over 2 seasons. Vaccine efficacy rates varied by respiratory disease type and RSV-LRTI subtype, as follows:

• RSV-LRTI: 67.2% (97.5% CI, 48.2-80.0);
• Severe RSV-LRTI: 78.8% (95% CI, 52.6-92.0);
• RSV-ARI: 52.7% (95% CI, 40.0-63.0);
• RSV-A: 80.5% (95% CI, 54.0-93.2); and
• RSV-B: 59.7% (95% CI, 35.8-75.5).

In 1-dose recipients, sustained efficacy against RSV-LRTI was also observed among patients aged between 60 and 69 years (65.4%; 97.5% CI, 40.4-80.9) and those aged between 70 and 79 years (74.9%; 97.5% CI, 48.4-89.2), those with at least 1 co-existing condition of interest (66.7%; 97.5% CI, 41.8-82.0), and those with pre-frail status (73.3%; 97.5% CI, 42.4-89.2).

Further analysis showed no additional efficacy benefit against RSV-LRTI among 1-dose recipients who were revaccinated at 1 year. Revaccination also conferred no additional efficacy benefit with respect to secondary outcomes.

The reactogenicity and safety profile (18-month follow-up period after dose 1) of the revaccination dose was comparable to that of the first dose, with mostly mild to moderate and transient adverse reactions, such as injection-site pain and fatigue, reported in both groups.

Limitations of this study include relatively low numbers of patients with frailty, patients aged 80 years and older, RSV-LRTI diagnoses, and RSV-related hospitalizations. Lastly, the sizes of the revaccination and single-dose groups in season 2 complicates the comparison of efficacy between the 2 seasons.

“Further research is needed to evaluate whether efficacy is maintained over more than 2 seasons and if extending the interval between initial vaccination and revaccination may enhance boosting,” the researchers concluded.

Disclosure: This research was supported by GlaxoSmithKline Biologicals SA, and multiple study authors declared affiliations with biotech, pharmaceutical, and or/device companies. Please see the original reference for a full list of disclosures.

This article originally appeared on Infectious Disease Advisor